1. Field of the Invention
The present invention relates to a coupling structure of a driven device that is installed in an internal combustion engine and is rotatably driven by the internal combustion engine, and more particularly, to a drive shaft coupling device that coaxially couples a driven shaft of the driven device with a drive shaft of the internal combustion engine.
2. Description of Related Art
Generally, supply pumps for supplying high-pressure fuel to a common rail of an automobile fuel system are similar to that as shown in FIG. 9. The supply pump has a camshaft 51, corresponding to a driven shaft, of a supply pump 50, corresponding to a driven device, that is rotatably driven by an internal combustion engine via transmission means 52 such as a pulley, a gear, or the like.
Automobile part manufacturers desire reducing the cost of common rail fuel injection systems installed in passenger cars. Additionally, there have been reductions in drive peak torque and the sizes of the supply pumps that transmit alternating pressures. Even though supply pumps have been made smaller and their torque has been reduced, a conventional drive system, that is, a system to drive the supply pump via a pulley or a gear, still has a high cost and still requires a large amount of space for its use.
Accordingly, the supply pump must be driven in such a manner that a camshaft of the supply pump must be coaxially disposed with a drive shaft of the internal combustion engine. In this case, it is necessary that an Oldham coupling be utilized between them to account for the shaft misalignment of the drive shaft of the internal combustion engine with the camshaft of the supply pump.
To better explain the problem, an embodiment of the Oldham coupling will be hereinafter described with reference to FIG. 10. An Oldham coupling 60 shown in FIG. 10 comprises a union 61 secured to the drive shaft of an internal combustion engine, a coupling plate 62 which is fitted into first grooves 61a formed in the union 61 in such a manner as to extend in a direction orthogonal to an axial direction. The coupling plate 62 further has arm portions 62a slidable along the first groove 61a, and an Oldham projection 63 which is slidably fitted into a second groove 62b formed in the coupling plate 62 in such a manner as to extend to a direction orthogonal to the arm portion 62a. The Oldham projection 63, as shown in FIGS. 11A and 11B, is formed at an end of the camshaft 51 of the supply pump 50.
In the Oldham coupling 60 in the above structure, the Oldham projection 63 is narrow in width, because the width of the Oldham projection 63 is decided by the diameter of the camshaft 51. When the Oldham projection 63 is narrow in width like this, an edge 63a, which is a hatched section of FIG. 10, of the Oldham projection 63 collides hard with the second groove 62b of the coupling plate 62. Furthermore, the Oldham projection 63 is fitted into the coupling plate 62 disposed in the union 61. As a result, oil does not get into a joint sliding portion of the Oldham projection 63 even if the oil is sprayed from the outside in a jet. This creates a lubrication deficiency. Accordingly, since the Oldham projection 63 and the coupling plate 62 become heavily worn down, backlash, that is, essentially a gap, occurs in the joint portion between the Oldham projection 63 and the coupling plate 62. When backlash is present, there is a possibility that an impact load occurring in the bottom of the Oldham projection 63 will damage the Oldham projection 63. The impact of any backlash also causes noise.
Furthermore, there is a possibility that dust and shavings generated by contact and wear will adversely affect other parts and devices. In other words, the oil containing the wearing dust will be circulated to an oil pump, for example. This may cause a malfunction in the oil pump and/or clog oil pump paths. Therefore, conventionally, it is undesirable to drive the supply pump, the camshaft of which is disposed coaxially with the drive shaft of the internal combustion engine, due to the defects described above.
The supply pump is adopted as one example of the driven device, as shown by the above, but many other types of driven devices cannot adopt a structure in which the driven shaft of the driven device is disposed coaxially with the drive shaft of the internal combustion engine, due to the reasons described above.